COVID-19 and smoking: is nicotine the hidden link?

Leung et al. [1] have recently published, in the European Respiratory Journal , a paper on the expression of angiotensin-converting enzyme II (ACE-2) in the small airway epithelia of smokers and COPD patients, discussing its effects on the risk of severe coronavirus disease 2019 (COVID-19). The authors found an increased expression of the ACE-2 gene in the airways of subjects with COPD and in current smokers. Indeed, a recent systematic review reporting data on the smoking habits of patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), concluded that smoking may be associated with a negative progression of the disease and with the adverse outcome [2]. Nicotine via alpha7-nicotinic receptor induces ACE-2 overexpression in human bronchial epithelial cells (HBEpC)